This application is a continuation of International Patent Application No. PCT/DE95/01487, filed Oct. 26, 1995. The invention relates to a process for early detection of oil spills in the sea and for aiding navigation with respect to ship traffic, to avoid collisions between ships, and between ships and icebergs.
Observation and detection of oil spills is routinely carried out on several coasts (for example, the North Sea coast in the Netherlands). In the latter case, so-called "Coast Guard" planes are used which, however, because of their limited operating range can observe only a relatively narrow coastal strip of approximately 2 to 3 nautical miles. Moreover, because the detection of oil spills is carried out visually by the pilots, this method can be used only during the day and in favorable weather conditions.
In a pilot program, an oil detection project was carried out at the German North Sea coast by means of airplanes equipped with a Synthetic Aperture Radar Sensor ("SAR"). Although, this radar sensor can also detect oil spills at night, once again because of the limited operating range of the planes, a routine observation of larger sea areas is also not possible.
The ERS-1 and ERS-2 satellites operated by the European Space Agency are equipped with comparable radar sensors. Because of their global coverage, they also permit oil detection in areas outside the coastal strip of a width of 2 to 3 nautical miles. The effective width of the strip covered by these sensors is approximately 100 km. However, the repetition rate of these satellites (that is, the time period between successive observations of a specific point on the earth's surface is approximately 13 days (at night and during the day).
Routine detection of possible oil spills and the identification of the potential causes (that is, an identification of the vessel(s) involved) will be possible only when the repetition rate can be reduced to approximately three hours, so that the local distance between the position of the oil spill and the position of the ship in question can be reduced to less than 50 km. Such a repetition rate, however, would require a satellite constellation of the ERS type with approximately 100 individual satellites. Because of the high procurement costs of the satellites and the associated operating costs on the ground, the resulting financial expenditures for such a system are out of proportion to the economic savings potential (such as the costs for removing the oil, costs for eliminating ecological damage).
An object of the invention is to provide an overall system which uses known components to detect icebergs and oil spills (as well as the causes of the latter) at sea in connection with a monitoring and control of ship movements and avoiding possible collisions between ships, and between ships and icebergs.
This object is achieved according to the invention by monitoring the position of ships, icebergs, and oil spills by means of a satellite based observation system equipped with dedicated synthetic aperture radar sensors (SAR). Position information acquired by the satellites is transmitted to a central facility, which continuously evaluates this information to warn of possible collisions, and to determine the cause of oil spills. The number of satellites required for such routine detection of possible oil spills and the identification of the potential causes is reduced by widening the accessible observation area on the ground. That is, an increase in the width of the observation strip permits an approximately proportional reduction in the number of satellites. Such widening can be achieved by:
the mounting of a second radar sensor so that a left-hand and a right-hand strip can be observed on the ground; or PA1 turning the satellite transversely to the flight direction in order to direct the sensor to a target area to be observed. This will be supported by modifying the pulse repetition frequency of the SAR sensor to take into account the antenna depletion angle. PA1 Recognition of oil spills and icebergs at sea by means of satellite-supported phased array microwave instruments with an accessible strip of approximately 1,000 km on the ground; PA1 precise determination of the position of the ships connected to the system; PA1 communication between the ships connected with the system and the satellites pertaining to the system, such as the communication between the satellites and a monitoring center. PA1 A substantial reduction in the number of required satellites in comparison to the technology used today; PA1 central monitoring and reconstruction of ship movements at sea; PA1 a central clear identification of a ship which may have caused an oil spill; PA1 timely central establishment and targeted dissemination of warnings concerning possible collision courses (ship/ship and ship/iceberg).
By mounting a second sensor as provided in the first alternative, the number of satellites can be reduced by approximately one half while by turning the satellite according to the second alternative, the number of satellites can be reduced approximately by a factor five. If both measures are combined, a theoretical reduction factor of approximately 10 can be achieved. However, frequent turning of the satellite toward the target area to be observed requires very high on-board energy (fuel) expenditures, which reduces the orbit life of the satellite correspondingly. Furthermore, the time required to turn a satellite is several minutes. Since no observations can be carried out during this time, the resulting effective reduction factor is considerably lower than the theoretical factor (approximately 2 to 3).
In order to overcome this difficulty, the method according to the invention uses synthetic aperture radar sensors which have individual beaming devices (so-called phase array antennas), permitting an electronic pointing of the sensor transversely to the flight direction within a few milliseconds. This feature will result in an accessible and an effective observation strip. The effective strip represents the swath on ground, which can entirely be monitored by the SAR sensor at a time, also known as effective field of view of the sensor. Modifying the phases between the individual array antennas of the sensor will allow to shift the field of view of the sensor transversely to the flight direction. The resulting upper and lower border of these possible field of view directions represent the accessible swath on ground.
By means of a suitable arrangement of the individual beaming devices, the accessible observation strip on the ground can therefore be enlarged to approximately 400 to 500 km; the effective observation strip will then measure approximately 50 to 100 km. By using a right-hand and left-hand radar sensor, these values can be doubled. Thus, the accessible observation strip will measure approximately 1,000 km and is therefore larger by the factor 10 than in the case of today's ERS satellites.
The repetition rate of such a satellite will then be approximately 1.3 days or 32 hours. In order to reach the required repetition rate of, for example, 3 hours, a constellation of only 10 satellites would therefore be required. If, furthermore, only the northern sea regions starting at approximately 30 degrees latitude (such as the North Atlantic) are to be observed, (and assuming that a polar orbiting satellite is used) the required number of satellites is reduced to approximately 9 due to the convergence of the observation paths of successive orbits as they approach to pole.
The process according to the invention facilitates the following functions:
The advantageous linking of these individual functions to form an overall system permits: